


Time-out

by armethaumaturgy



Series: Reqs [10]
Category: Undertale (Video Game)
Genre: Banter, Ecto-Genitalia (Undertale), Explicit Sexual Content, Killer (Killertale) - Freeform, M/M, Nightkiller - Freeform, Nightmare (Dreamtale) - Freeform, Nightmare/Killer - Freeform, Possessive Behavior, Sex During A Battle, Vaginal Fingering, Vaginal Sex
Language: English
Status: Completed
Published: 2021-03-09
Updated: 2021-03-09
Packaged: 2021-03-16 11:35:09
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,007
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29949393
Author URL: https://archiveofourown.org/users/armethaumaturgy/pseuds/armethaumaturgy
Summary: “What is the meaning of this, Killer?” he asked, eyesocket narrowed as he all but spat the name out.Impossibly, Killer’s grin got wider. “Gonna fuck you into this wall, boss,” he said, and it would’ve sounded conversional, if not for the faint crimson glow from his shorts.Nightmare regarded him with a flat stare for a moment. “Really? Couldn’t you have waited?”
Relationships: Sans/Sans (Undertale)
Series: Reqs [10]
Series URL: https://archiveofourown.org/series/2151672
Comments: 10
Kudos: 175





	Time-out

**Author's Note:**

  * For [carelesscreativity](https://archiveofourown.org/users/carelesscreativity/gifts).



> written for the lovely @nBHerE0 on twitter! ♥♥

Nightmare steadied himself with two of his tentacles, feet skidding in the dirt from being pushed backwards. A third one snapped the glowing blue arrow it had caught mid-flight.

 _Dream’s aim had ever been impeccable,_ he thought wryly.

The tentacle’s tip sharpened, ready to return the favor, but Dust stepped in front of him, raising what very well accounted for a wall of bones. They cracked under the barrage of more arrows, but held, and Dust tisked. 

Nightmare didn’t have the time to ponder what his exasperation meant; the very next moment, his back was against a wall, Dust’s figure lost behind the corner of the alley he found himself in.

Only his self-control winning against instincts was what allowed Killer to not end up skewered by his flicking tentacles. There was the usual grin of his, plastered to his skull, but it had an edge to it. From the main street, Nightmare could hear Cross and Ink shouting at each other.

He’d never really been a fan of universes that reached the surface. Too much concrete for his taste. It bit into his back where he was pinned and his shoes squeaked on it under him.

“What is the meaning of this, Killer?” he asked, eyesocket narrowed as he all but spat the name out.

Impossibly, Killer’s grin got wider. “Gonna fuck you into this wall, boss,” he said, and it would’ve sounded conversional, if not for the faint crimson glow from his shorts.

Nightmare regarded him with a flat stare for a moment. “Really? Couldn’t you have waited?”

“Nope,” was the immediate and too smug answer.

Killer was coated in blood and dust, and none of it was his, and the rest of their group was still fighting his _brother_ and his pals just meters away, and it was a ridiculous proposition, and Nightmare could have laughed. Instead, he growled and surged forward to click their teeth together into a kiss.

“Make it fast,” he hissed out in between further kisses, against Killer’s tongue trying to worm its way into his mouth.

“How ‘bout I made it _good_ instead?” Killer drawled, one hand snaking between them to rub against one of Nightmare’s pubic arches through his shorts. “Make something pretty for me, boss.”

There wasn’t a word of protest when the clothes filled out and Killer slipped his hand into the fabric, snapping the waistband against the cyan of the plush ecto before pulling them down, but Nightmare was glaring at him for the display. He let himself get pulled up against the wall, and Killer knew he was _letting_ him, knew that Nightmare trusted him enough to even consider this, knew that he could’ve had him on the ground, already dusting if he wanted, and there was something indescribable about that knowledge. It made up for the slight difference in height and let Killer slot his hips flush with Nightmare’s, to let him feel the bulge straining Killer’s own shorts.

The one and only indication that his boss was flustered by his actions was the way his tentacles curled around them, all but cocooning them from the rest of the world, from the sounds of battle and destruction. And maybe the dusting of cyan over his visible cheekbone, but Killer supposed he could chalk that up to the way he was grinding his cock between Nightmare's splayed legs, no doubt putting pressure against his clit.

LV was heavy and heady in Killer’s bones, and the way Nightmare arched his neck, baring it for Killer’s hungry gaze, made him want to sink his teeth into the column of it, draw out marrow and make Nightmare beg for him.

So he did.

Leaning in made his SOUL press against Nightmare’s bosom. It was all Killer could do to muffle his groan as he bit down on a vertebrae. Nightmare gasped out against him, the taste of corruption mixing with marrow on Killer’s tongue, and his body felt like it was on fire.

When he shoved his shorts out of the way, the fabric too constricting, he found them soaked in cyan magic. The sight spurred him on, and he wasted no time in pushing two fingers into Nightmare’s soaked cunt, the ecto pliant around them even as it clenched. 

“Stars, you’re drenched,” he marveled, as if he didn’t do so every single time. Nightmare would’ve rolled his eyelight, but Killer thrust them in all the way, crooking them in a way that had his spine arching.

He gasped, hips arching into the phalanges, chasing that same angle. Killer’s palm pressed against his clit and provided just the right amount of pressure when he moved, only making the pleasure that much sweeter.

All too soon, Killer pulled them out, though, and Nightmare lamented their loss with a quiet whine.

“Done teasing?” he asked, putting conscious effort into not sounding strained. His entrance clenched down on nothing, feeling too empty.

“Would love to keep it up, but we’re on a schedule.” Killer snorted, but Nightmare couldn’t even begin to ask what he meant before he slotted their hips together again, dragging the length of his cock along Nightmare’s slit, through the slick in teasing little thrusts.

For all his talk of not teasing anymore, it sure felt like it was just that.

Finally, Killer pushed in with one smooth move, Nightmare’s body accepting him like they belonged together, entrapping him in a velvety vice. It was hot, it was wet, and it was perfect. Nightmare sighed out his bliss.

“Hehe, y’like that, boss?” he asked, hot breath over the bite on Nightmare’s neck only serving to make him shiver. His walls were clenching and unclenching sporadically around him, and he wasn’t even moving yet. “Y’like being fucked like this? In an alleyway like a whore? In the middle of a battle, when everyone could hear us?”

Nightmare bit out a groan, hands gripping onto Killer’s shoulders for purchase. Killer’s hand, in turn, squeezed at one of his thighs and pulled it around his hips; Nightmare caught on, hooking his legs around Killer’s hips and locking his ankles over the small of his back.

“Betcha would’ve let me jump your bones the moment the fight was over,” Killer continued, pulling his hips back despite Nightmare squeezing down, like he didn’t want to let him go. “Bet you still will. Just like _every time.”_

Nightmare groaned when he pushed back in, fingers digging into his hoodie so tight he was ripping holes in the fabric, but Killer didn’t seem to mind. “Killer,” he sighed out, a borderline moan.

Killer set a pace, holding Nightmare’s ass in one hand and using the other to fondle one of his breasts over the stretched shirt, and it was like a dam breaking. Nightmare’s panting was punctuated with gasps and quiet moans, and Killer’s name was like a mantra on his tongue.

Loath as he was to shut him up, Killer kissed him again, swallowing all those sinful noises at their root.

“Careful, moonlight,” he teased, smirking when he felt Nightmare shiver at the nickname. He adjusted his grip on the other skeleton. The next thrust pulled a stuttered half-scream out of the guardian, unheeding to Killer’s words. Killer made sure to keep that angle, even as he said, “Don’t want the other to hear you, do you?”

Nightmare glared at him, though it was not as effective as it usually would have been, not with the way his hips canted into each one of Killer’s thrusts.

“No one _would_ hear us if you could keep it in your pants for ten more minutes,” he said, but that, too, was intersped with breathy gasps and near whimpers.

“But where’s the fun in that?” Killer’s cock dragged against Nightmare’s wall in the best of ways, the angle hitting the most sensitive spot with every minute shift of his hips, like his cock was made just for it. Nightmare’s thighs were shaking where they bracketed his hips. “Damn,” Killer chuckled, “Close already, moonlight?”

Nightmare deigned to ignore the obvious jab to get a rise out of him and instead leaned up to kiss his stupid lover again. With the cover of his tentacles, he could almost pretend they were alone, but Killer seemed adamant about reminding him that they were, in fact, _not._

“They know,” he said, face so close that Nightmare could feel each of his labored breaths on his wet teeth, still parted, still connected to Killer’s tongue by a string of their mixed saliva, red and cyan and _filthy._ Killer shoved his hand under his shirt to tease his breast properly, phalanges teasing over his nipple and making sparks of pleasure race through him. “Dusty, Horror, Criss-cross, they all know we’re doing this.”

Nightmare choked on a moan, screwing his eyesocket shut. Killer’s cock hit the end of his magic, his pace hard and fast, and heat pooled low in Nightmare’s pelvis, coiled tight like a spring ready to jump, like a livewire.

“They’re fighting so you can have this,” Killer told him, and something primal in Nightmare was so incredibly _pleased_ at hearing that that he choked on Killer’s name as it clawed his way out of his throat alongside another moan. “They’d give their lives just so we could do this. Just so you could be fucked the way you love.”

The coil in Nightmare shaped and he came with a flash of white, mouth opening in a soundless scream, unlike all the ones before it. Slick gushed between them, dripping down to the ground as Killer fucked into him through it, each thrust prolonging his orgasm, and when he put two fingers at his clit and rubbed it, with almost no friction from all the slick, it was almost _too_ much.

He shook in Killer’s hold, sated, all but floating in the sensations as Killer used his pliant, lax body, lifting him in time with his thrusts, made short and jerky with Nightmare’s release making his insides tighter than before.

“M-Moonlight,” Killer breathed out, closing his sockets as his hips stilled, buried as deep inside his cunt as he could be. The feeling of scalding hot magic filling him was a familiar and welcome one, a physical proof of his lover’s pleasure that a part of Nightmare found solace in.

He clung to Killer, even as the other pulled out and cum gushed out of him, splashing the cobbled ground in a mixture of red and cyan, swirling together to make a bright purple shade. Nightmare, in his hazy mind, was reminded of Cross’ magic, of all things.

He was still shaking when Killer’s hands moved to his hips to steady him as he was placed onto his feet, tentacles uncoiling from each other to brace him against the wall. His mind slowly returned to him, and with it, the sounds from the other street, the voices of both his other boys and their adversaries too faint to make out any specific words spoken, but clear enough to recognize.

The knowledge that his brother had no doubt felt their emotions and the sheer amount of _trust_ between them made Nightmare giddy in a selfish way.

When he looked down, he could see his shorts ruined with slick, and Killer wasn’t much better off. But instead of anything _sensible,_ because when had Killer ever been _sensible,_ he stepped out of his shorts and kicked them off to the side.

“What the hell are you doing?” Nightmare asked, frowning. His answer was a razor-sharp grin as Killer pulled out two bundles from his inventory, and held one out to Nightmare.

“Gonna rejoin the fray. How about you, moonlight?”

As Nightmare took the bundle — which turned out to be a clean pair of shorts — Killer shimmied into his own. 

“You were surprisingly prepared for this,” Nightmare commented, but exchanged his soiled shorts for the clean ones nevertheless. Killer shrugged, his grin never leaving. There was a measure of lopsidedness to it as Killer pulled out his knife.

“Told you all the others knew.”

**Author's Note:**

> my twitter is @esqers ♥


End file.
